Cyberweapons and sophisticated hacking pose a greater threat to the United States than the risk of physical attacks, Homeland Security Secretary Kirstjen Nielsen said Wednesday while urging state election officials to add more safeguards to their voting systems.

In a speech timed to next week’s anniversary of the 9/11 terrorist attacks, and amid worries about interference in coming U.S. elections, Nielsen said the Department of Homeland Security is facing down an array of cyberthreats from hostile foreign governments, extremist groups and transnational criminals.

“DHS was founded fifteen years ago to prevent another 9/11. I believe an attack of that magnitude is now more likely to reach us online than on an airplane,” she said. “Our digital lives are in danger like never before.”

American election systems continue to be a prime target for foreign powers, Nielsen warned. Echoing the U.S. intelligence community’s consensus that Russian president Vladi­mir Putin interfered in the 2016 contest, Nielsen said DHS cannot allow another “direct attack on our democracy.”

The agency has added electronic monitoring sensors to districts covering 90 percent of registered voters, Nielsen said, but she urged state election officials to reassure voters by creating printed records of digital ballots.

“Today, I am calling on every state in the Union to ensure that by the 2020 election, they have redundant, auditable election systems,” she said. “The best way to do that is with a physical paper trail and effective audits so that Americans can be confident that — no matter what — their vote is counted and counted correctly.”

Nielsen’s advisers promoted Wednesday’s speech at George Washington University as a road map for her vision of the department’s evolution. The agency, with a $48 billion budget and more than 240,000 employees, is shifting at her direction from a “counterterrorism posture” to a wider “counterthreat” approach, Nielsen said, to respond more nimbly to hackers and digitally savvy terror groups as well as America’s rivals.

“Threats to the U.S. from foreign adversaries are at the highest levels since the Cold War,” she said, calling on lawmakers to elevate Homeland Security’s cybersecurity division — the National Protection and Programs Directorate — to a “full-fledged operational agency,” on par with other major DHS agencies such as U.S. Customs and Border Protection or the Transportation Security Administration.

The increase in risk from cyberattacks does not mean threats from cruder, physical ones have subsided, Nielsen added, warning U.S. aviation remains a major target for extremist groups. Of particular concern is the possibility that terrorists will attempt to use drones to attack U.S. cities and infrastructure. Nielsen described such scenarios as “what keeps me up at night.”

“Imagine a drone dropping a small bomb on a busy street. Or in a football stadium. Or releasing chemicals on a crowd at an outdoor concert,” she said, imploring Congress to give DHS more authority to track and intercept “dangerous drones.”

Nielsen said America’s enemies in the real and virtual worlds want “to disrupt our way of life.”

“The pace of innovation, our hyperconnectivity and our digital dependence have opened cracks in our defenses, creating new opportunities and new vectors through which these nefarious actors can strike us,” she said. “The result is a world where threats are more numerous, more widely distributed, highly networked, increasingly adaptive, and incredibly difficult to root out.”

In response, the United States must develop a security infrastructure based on what she called “relentless resilience.”

Before joining the Trump administration, Nielsen was a senior fellow at the university’s Center for Cyber and Homeland Security and worked as a private cybersecurity consultant. She was handpicked for the role last year by White House chief of staff John F. Kelly and was on the receiving end of President Trump’s anger earlier this year when illegal migration surged.

Nielsen approved the “zero tolerance” crackdown at the border this spring that ramped up criminal prosecutions and separated more than 2,500 migrant children from their parents. She did not mention immigration enforcement in her speech Wednesday or take questions from the audience or media.